Droplet actuators are used to conduct a wide variety of droplet operations. A droplet actuator typically includes two substrates separated by a gap. The substrates are associated with electrodes for conducting droplet operations. The gap includes a filler fluid that is immiscible with the fluid that is to be manipulated on the droplet actuator. The formation and movement of droplets in the gap is controlled by electrodes for conducting a variety of droplet operations, such as droplet transport and droplet dispensing. At least one of the surfaces is typically made from a transparent material, such as a glass top substrate. Among other things, when glass is used, adding features to the glass, such as openings for loading fluid into the gap, can be complex and expensive. There is a need for alternative droplet actuator structures that are easier and less expensive to manufacture while providing the same or better functionality as glass top substrates.